1. Field of the Invention
The present invention relates to an image forming apparatus and to a method of controlling this apparatus.
2. Description of the Related Art
An image forming apparatus such as a copier or multi-functional peripheral generally comprises a plurality of subsystems such as a main controller for controlling the overall image forming apparatus, a scanner for reading in an image and a printer for forming an image on paper. It has become commonplace, in recent years for such an image forming apparatus to be connectable to a network. A network-connected image forming apparatus receives print data, which has been transmitted from a plurality of personal computers or servers, via a network, and performs printing in accordance with the print data received.
Further, if the image forming apparatus is not issued an operation request in excess of a fixed period of time, control is exercised to automatically cut off the supply of power to the scanner or printer and effect a transition to a power save mode in order to reduce power consumption. Generally, in the power save mode, the supply of power to the main controller is maintained. Control is exercised by the main controller in response to an input of a prescribed signal in such a manner that the image forming apparatus is restored from the power save mode to the normal power supply state.
In order to achieve a further power saving, it has been proposed to perform finer control of power even in the main controller, supply power only to a communication control unit that accepts communication from external equipment and cut off supply of power to other controllers. In this case, since power is supplied to the communication control unit, supply of power to the entirety of the main controller can be started in response to a communication request from external equipment and the communication request can be processed.
An overview of a power saving operation in an ordinary image forming apparatus of the above-described kind is illustrated in FIG. 7. In FIG. 7, step S1000 represents a standby state in a normal mode. Step S1000 represents a state in which the apparatus awaits a processing request such as a print request from outside the image forming apparatus or from a console. In a case where the setting is such that a transition is made to the power save mode if there is no processing request over a fixed period of time, a timer for measuring the length of time over which there is no input signal (processing request) from the outside operates within the apparatus. If a processing request of some kind is issued, control proceeds to step S1001, where the requested processing is executed, and then returns to step S1000. At this time, the value measured by the timer that measured the length of time without a processing request is cleared and measurement is re-started from the moment the requested processing ends.
In the standby state (i.e., during the absence of a processing request), reference is had to the timer value at step S1002 and it is determined whether a transition to the power save mode should be made. If it is determined that there will be no transition to the power save mode (i.e., if the timer value has not attained a prescribed time), then control returns to step S1000.
The above-described processing is repeated. If it is determined at step S1002 that a transition is to be made to the power save mode (i.e., if the timer value indicates elapse of the prescribed time), then processing for transitioning to the power save mode is executed at step S1003. For example, processing for saving necessary data from a DRAM to a non-volatile storage medium such as a hard disk is executed and supply of power to part of the apparatus is halted. Control then proceeds to step S1004. This step represents the standby state in the power save mode. As mentioned above, in this state part of the power supply is shut down and power consumption is reduced. In the power save mode, power is supplied at least to the communication control unit of the main controller. Issuance of a new processing request is monitored at step S1004. If a new processing request is issued, control proceeds to step S1005, at which the power save mode is terminated. That is, supply of power is resumed to the components to which supply of power was stopped and a transition is made from the power save mode to the normal mode. At step S1001, the apparatus operates in the standby state in the normal mode after the processing in response to the processing request is executed.
A variety of processing requests are issued to the network-connected image forming apparatus. For example, a client personal computer on the network periodically transmits a communication request for monitoring whether or not the image forming apparatus is in a state in which it is capable of printing. If the image forming apparatus is operated normally whenever there is such a request, the length of time during which the apparatus is in the power save mode is shortened and the power-saving effect is diminished. Methods set forth below have been proposed as methods of solving this problem.
The specification of Japanese Patent Application Laid-Open No. 8-324071 describes an image forming apparatus in which, when the power save mode is in effect, power is supplied only to a communication control unit and is cut off from other controllers, printer and scanner. Japanese Patent Application Laid-Open No. 8-324071 is such that if a communication request from external equipment is detected, the communication control unit determines whether or not to supply power to other controllers, printer and scanner based upon the communication request. Supply of power to each of the components is resumed in accordance with the result of this determination.
Further, the specification of Japanese Patent Application Laid-Open No. 2001-180083 describes a power-saving technique in a printing apparatus having first communication interfaces connected to external equipment in 1:1 correspondence, and a second communication interface connected in common with a plurality of items of external equipment. Japanese Patent Application Laid-Open No. 2001-180083 is such that if the first communication interfaces have been connected, a power supply of control means is cut off when the power save mode is in effect. Further, if the second communication interface has been connected, the operating blocks of the control means are shut down without cutting off power to the control means when the power save mode is in effect.
In Japanese Patent Application Laid-Open No. 8-324071, however, the communication control unit monitors whether information as to whether supply of power should be started is monitored is received at all times. Even in the power save mode, therefore, it is necessary to supply power at all times to a CPU, ROM and RAM, etc., that construct the communication control unit. A problem, therefore, is that a comparatively large amount of power is consumed.
Further, Japanese Patent Application Laid-Open No. 2001-180083 is such that when the apparatus has been connected to a network (second communication interfaces), a clock is halted but power continues to be supplied. Power is consumed as a result. Demand for power saving has grown more intense in recent years. Even if circuits cease operating (even though the clock is halted), leakage current consumed by the circuits is not negligible.
Furthermore, the Japanese Patent Application Laid-Open No. 2001-180083 is such that if data of some kind is received from the network, the content of the received data is analyzed and it is determined whether to restore operation from the power save mode. The clock of the control unit such as a CPU is resumed in order to accomplish this. Accordingly, if reception of data from the network is performed frequently, the controller is almost always in the normal operating mode. Ultimately, consumption of power in the power save mode is great, just as in the case of Japanese Patent Application Laid-Open No. 8-324071.